1. Field of the Invention
The present invention relates to an apparatus and method for estimating an arousal level of a vehicle driver by detecting vehicle behavior such as a lateral displacement of a vehicle.
2. Background Art
A technology for preventing car accidents caused by decline in driver""s arousal level is one of most important developmental subjects of today from the view point of vehicle safety. In recent years, studies for detecting drowsiness or arousal level of vehicle drivers, developments of techniques for warning them against falling into a drowsy state are actively undertaken. When a driver""s arousal level declines, especially when a vehicle travels at high speeds, serious accidents may happen. Even if he or she does not reach such drowsy state, drowsiness induces him or her to an absent-minded state which inhibits a quick averting operation, this leading to accidents.
Japanese Patent Application Laid-open No. Toku-Kai-Hei 5-58192 discloses a technique in which so-called xe2x80x9cdozing at the wheelxe2x80x9d is detected based on low frequency components in operation quantity. In this disclosure, operation quantities such as steering angle, lateral displacement of a vehicle and the like are monitored consecutively and low frequency components in frequency spectrum of the operation quantity are extracted. On the other hand, low frequency components in frequency spectrum of operation quantity at normal operations are memorized as sample data beforehand. Then, the low frequency components after a specified time elapses from the start of the vehicle are compared with those sample data. If a difference between the low frequency components and the sample data exceeds a predetermined value, it is judged that the driver dozes at the wheel.
However, the sample data which are used for the judgment reference are ones collected under a certain transport environment (weather, road surface conditions, time, degree of traffic jams, vehicle speed and others). If the running condition changes, the judgment whether or not the driver is in a dozing state is accompanied by errors. That is, this background art has a problem that, when the running condition changes in a large scale, it is difficult to obtain a correct judgment as to whether or not the driver is in a dozing state.
It is an object of the present invention to provide an arousal level estimating apparatus capable of accurately judging the arousal level of a vehicle driver without being affected by running circumstances and vehicle speed.
To achieve the object, a driver""s arousal level estimating apparatus comprises an operation quantity detecting means for continuously detecting an operation quantity of the vehicle, a power calculating means for calculating a frequency component power by applying a frequency conversion to the operation quantity, a low frequency domain establishing means for establishing a low frequency domain lower than a predetermined reference frequency, a high frequency domain establishing means for establishing a high frequency domain higher than the reference frequency, an evaluation value calculating means for obtaining a first integral of the frequency component power in the low frequency domain, for obtaining a second integral of the frequency component power in the high frequency domain, and for calculating an evaluation value based on the first integral and second integral, and a judging means for judging an arousal level of the driver based on the evaluation value.